The function(s) of a purified Ca to the 2nd power ion-binding protein (CDR) from brain will be sought by a variety of rationales. A CDR-dependent form of phosphodiesterase from brain will be purified to homogeneity and characterized physically and kinetically. The subunit structure of the enzyme will be examined by SDS acrylamide gel electrophoresis. Antibodies will be prepared against the purified phosphodiesterase and used both to study its cellular localization in brain by histochemical immunofluorescence and its relationship to other forms of phosphodiesterase in brain. The in eraction of Ca to the 2nd power ion . CDR and lipid activators with the phosphodiesterase will be examined by circular dichroic spectrophotometry. Additional agents to those already identified will be sought which possess activity as Ca to the 2nd power ion - independent activators or inhibitors of the Ca to the 2nd power ion . CDR dependent activation of the phosphodiesterase. The Ca to the 2nd power ion . CDR modulation of the detergent-dispersed adenylate cyclase from brain will be studied kinetically. The Ca to the 2nd power ion-dependent modulation by CDR of a particulate adenylate cyclase from a clonal line of glial tumor cells (C-6) will be contrasted with the detergent-dispersed enzyme. Studies will be directed to examining the possible role of CDR in hormone activation and to establishing whether CDR modulation is a general charcteristic of adenylate cyclase or is restricted to specific forms. The relationship among Ca to the 2nd power ion metabolism, CDR and cyclic nucleotide metabolisms will be explored in tissue culture systems containing various CDR-modulated enzymes of cyclic nucleotide metabolism. The possible involvement of CDR in modulation of additional, as yet unidentified, enzymes will be examined. BIBLIOGRAPHIC REFERENCES: Brostrom, C.O., Huang, Y.-C., Breckenridge, B. McL., Wolff, D.J., Identification of a calcium-binding protein as a calcium-dependent regulator of brain adenylate cyclase. Proc. Natl. Acad. Sci. U.S.A., "72," 64-68 (1975). Huang, Y.-C., Wolff, D.J., Brostrom, C.O., Properties of a brain adenylate cyclase regulated by a Ca to the 2nd power ion-binding protein. Fed. Proc., "34," 517 (1975).